This invention relates generally to a method for controlling a process such as a planarization process in a multi-zonal processing apparatus and more particularly to a method for reconstructing the initial condition of an incoming work piece to be processed in that apparatus and to a method for controlling a process implemented on that work piece by utilizing the initial condition reconstruction. In accordance with a specific implementation, the invention relates to a method for reconstructing the initial thickness profile of an incoming work piece to be planarized and to a method for planarizing a work piece by utilizing the profile reconstruction as applied to a multi-zonal planarizing apparatus such as a multi-zonal chemical mechanical planarization apparatus.
Many types of processing apparatus include a plurality of zones within each of which some processing variable can be controlled in order to achieve some desired process result when a work piece is processed in the apparatus. For example, the processing apparatus may permit a variable or parameter such as pressure, temperature, voltage, current, or the like to be separately set in each of the plurality of zones to achieve a predetermined parameter distribution profile across the work piece. The predetermined profile, in turn, is intended to achieve a repeatable and predetermined result across the surface of the processed work piece. The process being controlled may be, for example, a polishing process, a planarization process such as a chemical mechanical planarization (CMP) process, a deposition process, or any other process practiced in an apparatus having a plurality of zones in which a process parameter can be adjusted in the various zones of the apparatus.
As an example, the manufacture of many types of work pieces requires the substantial planarization of at least one surface of the work piece. Examples of such work pieces that require a planar surface include semiconductor wafers, optical blanks, memory disks, and the like. One commonly used technique for planarizing the surface of a work piece is the chemical mechanical planarization (CMP) process, a process commonly practiced in a multi-zonal processing apparatus. In the CMP process a work piece, held by a work piece carrier head, is pressed against a moving polishing pad in the presence of a polishing slurry. The mechanical abrasion of the surface combined with the chemical interaction of the slurry with the material on the work piece surface ideally produces a surface of a desired shape, usually a planar surface.
The construction of the carrier head of a CMP apparatus and the relative motion between the polishing pad and the carrier head have been extensively engineered in an attempt to achieve a desired rate of removal of material across the surface of the work piece and hence to achieve the desired surface shape. For example, the carrier head generally includes a flexible membrane that contacts the back or unpolished surface of the work piece and accommodates variations in that surface. One or more pressure chambers are provided behind the membrane so that different pressures can be applied to various zones on the back surface of the work piece to cause desired variations in polishing rate across the front surface of the work piece. The carrier head also generally includes a wear ring that surrounds the membrane and the work piece and that pre-stresses or pre-compresses the polishing pad to protect the leading edge of the work piece. The pressure applied to the wear ring may also be adjusted (providing an additional zone) to aid in determining the polishing rate near the edge of the work piece.
The incoming work piece that is to be planarized generally has a non-uniform surface. That is, the work piece itself or a layer of material on the surface of the work piece has a non-uniform thickness. To achieve the desired (usually planar) final surface, the CMP process must be performed in a substantially non-uniform manner taking into account both the initial variation of material thickness across the work piece surface and the desired final shape. The initial pre-CMP distribution of material thickness and the desired post-CMP thickness determine the required distribution of CMP polishing rate and hence the required distribution of pressure in the various zones of the multi-zonal processing apparatus. Accordingly, to achieve the desired post-processing result, the initial pre-processing thickness distribution must be known or must be determined.
Heretofore there has not been a practical method for determining the surface characteristics of the incoming work pieces. Accordingly, a need exists for a method for determining the surface topology of the incoming work pieces, especially in an efficient and process worthy manner, so that the proper parameter values can be set in the various zones of a multi-zonal processing apparatus in order to achieve the desired final, post-processing surface topology. More generally, a need exists for a method for determining the pre-processing condition of a work piece that is to be processed in a multi-zonal processing apparatus so that a process parameter can be established in each of the zones of the apparatus to achieve the desired post-processing condition for the work piece. Additionally, a need exists for a method to process a work piece in a multi-zonal processing apparatus, such as a CMP apparatus, including properly and efficiently characterizing the pre-processing conditions of the work piece and using such characterization to determine the appropriate value to set for a process parameter in each of the zones of the multi-zonal processing apparatus.